In the manufacture of semiconductor devices, the surface of semiconductor wafers must be cleaned of wafer contaminants. If not removed, wafer contaminants may effect device performance characteristics and may cause device failure to occur at faster rates than usual.
One system used to remove wafer contaminants is commonly referred to as a scrubber. In at least one type of scrubber, semiconductor wafers are scrubbed simultaneously on both sides by a pair of brushes. While the wafer is being scrubbed simultaneously on both sides, the wafer is held in place and rotated so that the entire surface of the wafer is cleaned.
A wet processing system such as the scrubber described above comprises several distinct stations or modules. Each module is typically enclosed in a box-like structure which comprises the appropriate processing apparatus for that station. For example, a scrubber may comprise a load or send station, one or more scrub stations, a spin rinse and spin dry station, and an output station.
A load or send station typically comprises a platform for holding a cassette of wafers, an elevator for lowering and raising the cassette, and sensors for sensing the presence of a wafer. Additionally, the load station may comprise sprayers to spray the wafers with filtered, deionized water (D.I. water) to keep them wet while they await processing. This is necessary where the previous operation, such as chemical mechanical polishing, leaves wet contamination (e.g., a slurry mixture) on the wafers, which, if dried, would be virtually impossible to remove.
A scrub station typically comprises one or more brushes, wheels (e.g., rollers) which grip and turn the wafer by its side during scrubbing and sprays or nozzles for dispensing chemicals.
A spin station typically comprises a nozzle for a final water rinse, a spinner for spin drying, and a lamp to provide heat assisted drying. A spin station may also comprise a nitrogen blowoff in addition to, or in place of, the heat lamp to assist drying. The spin station may also be used for a secondary or post cleaning process, such as a megasonic cleaning.
Finally, an output station comprises a platform for holding a cassette of cleaned and dried wafers. Additionally, one or more types of wafer transport mechanisms, such as rollers, belt conveyors, robotic arms, etc., are provided to transfer wafers within and between the stations.
During a cleaning process, the wafer lies flat on a wafer transport mechanism such as a conveyor mechanism, which moves the wafer into the brushes. While being scrubbed, the wafer is supported (or held horizontally, by the wafer transport mechanism, brushes, rollers, or a combination thereof. In one prior art type of scrubber, as a wafer is being scrubbed by brushes, at least one roller rotates the wafer so that the surface may be cleaned. The roller may include an abrasive material to clean the edge/bevel area of the area of the wafer while it rotates. The roller itself is being rotated about its central access by a motor. The rotary motion of the roller is transferred to the wafer when the edge of the roller comes into contact with the outer edge of the wafer.
In one prior art system, the rollers are positioned using swing arms, which when rotated, cause the rollers to make contact with the wafer. Because the swing arms rotate, the brush box must be large enough in size to allow for the movement. However, it is desirable to provide more accurate control of the swing arms. That is, what is needed is a way to position rollers more accurately.
While systems have been developed to perform various wet processing operations, many drawbacks exist in prior art systems. For example, in wet processing systems that use highly acidic chemicals (e.g., HF), any exposure by drippage or fume exhaust may be harmful to the operator. Such contact with the chemicals may occur when maintenance or repair to the system is performed. Where the fear of contamination exist, it is desirable to minimize the potential exposure. Also, in prior art processing systems using such highly acidic and dangerous materials, there were little or no backup systems to compensate for leaks. Therefore, if a leak occurs, an immediate shut down of the system is the only solution. However, by the time such a shutdown is recognized as necessary, contamination may have already occurred.
Furthermore, in wet processing systems, contamination may also occur due to build up on the inside of the station walls. As chemicals in the brush stations and other stations dry, flaking may occur which increases the level of contamination and may cause damage to the system. Thus, it is desirable to reduce the build-up that occurs on the station walls.
The present invention provides for an improved wafer processing system which may be used for highly-acidic processes. In such processes, the system of the present invention include features which provide increased safety. The processing system reduces or even minimizes build-up on walls of the processing system that may cause flaking and contamination. In one embodiment, the system of the present invention also allows the rollers to be positioned without swing arms.